John refers to his readers as the progeny of God, His beloved brood. The world at large is the brood of Satan, so it recognizes neither our Father nor us. While we are His children already, the fullness of what that means has not yet been revealed. Somewhere out in the future, this will be fully manifested. When Christ returns for us, we shall see His eternal form, and simply seeing this will transform us to be eternal like Him. People who are looking forward to that day work hard to shed their fleshly nature as much as possible, trying to be like Jesus.
(The pseudo-Christian cultists didn’t fight their fleshly nature at all.)
It’s one thing to miscalculate what God intends; that’s the nature of childhood. Nobody’s children are perfect. Otherwise, we’d call them something other than “children”. But people who sin habitually are diving deep into injustice. They are rejecting the Father’s dominion. They aren’t His kids; they are foreigners. Jesus came to open the divine covenant and rescue people from their fleshly natures. He had no sin; He was the mature adult Son of His Father. Thus, we who have accepted His offer aren’t habitual sinners. Habitual sinners have never encountered Jesus.
So there are two kinds of people in the world. Those who belong to Jesus strive to live just and righteous like He did. Everyone else belongs to sin; they are children of the Devil, because the Devil rejected his Creator’s will for him right from the start. That’s why God sent His Son — to clean up the damage the Devil had done. When God reclaims a soul from Satan, He gives that soul a spiritual nature it did not previously have. That soul can no longer be at peace with habitual sin; it’s contrary to who they are. Moreover, those who lack that spiritual nature, who still belong to the Devil, are quite obvious by how they live. They have no interest in pleasing the Father. Keep your eye out for anyone who treats any believer with contempt.
We should hardly be surprised that the spiritually dead folks don’t like us. Do you remember Cain and Abel? They were two different kinds of men; Cain had no power to overcome his fleshly annoyance at this brother’s holiness. Our power to love each other is the proof that we have moved from the Abyss into the Kingdom of Heaven. Those who fail to manifest that kind of sacrificial love for believers are still dead. That kind of self-centered spite is the root of murder. People who can hate believers have never experienced spiritual birth.
The reason we have any grasp on love at all is because of the example of Christ taking up His Cross. Following Him means having that same level of commitment; we are ready to die for our fellow believers. How would you call it “sacrificial love” if someone is unwilling to sacrifice so much as a little of the material goods of this world for a brother in the Lord? It’s not enough to say the right words, but we must act on those words and live that truth.
The power to sacrifice for a fellow believer is all the assurance we need that we belong to Christ. Don’t listen to a condemned fleshly conscience; God’s voice in our spirits is louder than such a false testimony. Eventually the conscience will learn the truth and cease to condemn us, and we will see clearly God’s favor on us. It gives us the confidence to bring our requests before Him, knowing that He wants what is best for us.
His will for us is that we submit fully to His Son, swearing our undying allegiance. And His Son said His royal law for us was to love each other as He loves us. The folks who keep that law can do so only because of His Presence in their souls. When we can recognize that Presence in our souls, it becomes our assurance in serving Him.